数组扁平化，去重，排序

var startArr = [
	[1, 1, 2],
	[3, 2, 5, 4],
	[4, 5, 4, 1],
	[1, 3, 8, 9, [44, 41, 15, [14, 7, 9, [25]]], 18],
];

1. es5

1.1 for

function flattern(arr) {
	var _arr = arr || [],
		fArr = [],
		len = _arr.length,
		item; // 循环判断内部是否是数组,如果是,继续进行扁平化

	for (var i = 0; i < len; i++) {
		item = _arr[i];

		if (_isArr(item)) {
			fArr = fArr.concat(flattern(item));
		} else {
			fArr.push(item);
		}
	}

	return fArr;

	function _isArr(item) {
		return {}.toString.call(item) === '[object Array]';
	}
}

1.2 map

function flatternMap(arr) {
	var res = [];
	if (!Array.isArray(arr)) {
		throw new Error('no Array');
	}
	arr.map(item => {
		if (Array.isArray(item)) {
			res = res.concat(flatternMap(item));
		} else {
			res.push(item);
		}
	});
	return res;
}

1.3 reduce

function flatterReduce(arr) {
	var res = [];
	if (!Array.isArray(arr)) {
		throw new Error('no Array');
	}
	return arr.reduce((prev, item) => {
		return prev.concat(Array.isArray(item) ? flatterReduce(item) : item);
	}, []);
}

2. es6

2.1 reduce

const flatterReduceEs6 = arr =>
	arr.reduce((prev, item) => {
		return prev.concat(Array.isArray(item) ? flatterReduceEs6(item) : item);
	}, []);

2.2 flat

arr.flat(Infinity);
Array.from(new Set(startArr.flat(Infinity).sort((a, b) => a - b)));